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RECEIVER CIRCUIT USING NANOTUBE-BASED
SWITCHES AND LOGIC
CROSS-REFERENCE TO RELATED
 This application claims priority under 35 U.S.C. § 119(e). to U.S. Provisional Pat. Apl. Ser. No. 60/581,075, filed on Jun. 18, 2004, entitled Non-Volatile Carbon Nanotube Logic (NLOGIC) Receiver Circuit, which is incorporated herein by reference in its entirety.
 This application is related to the following references:
 U.S. patent application Ser. No. 10/917,794, filed on Aug. 13, 2004, entitled Nanotube-Based Switching Elements;
 U.S. patent application Ser. No. 10/918,085, filed on Aug. 13, 2004, entitled Nanotube-Based Switching Elements With Multiple Controls;
 U.S. patent application Ser. No. 10/918,181, filed on Aug. 13, 2004, entitled Nanotube Device Structure And Methods Of Fabrication;
 U.S. patent application Ser. No. 10/917,893, filed on Aug. 13, 2004, entitled Nanotube-Based Switching Elements And Logic Circuits;
 U.S. patent application Ser. No. 10/917,606, filed on Aug. 13, 2004, entitled Isolation Structure For Deflectable Nanotube Elements;
 U.S. patent application Ser. No. 10/917,932, filed on Aug. 13, 2004, entitled Circuits Made From Nanotube-Based Switching Elements With Multiple Controls;
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled Nanotube-Based Transfer Devices and Related Circuits;
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled Integrated Nanotube and Field Effect Switching Device;
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled Receiver Circuit Using Nanotube-Based Switches and Transistors;
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled Nanotube-based Logic Driver Circuits;
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled Storage Elements Using Nanotube Switching Elements; and
 U.S. patent application Ser. No. not yet assigned, filed on date even herewith, entitled TriState Circuit Using Nanotube Switching Elements.
BACKGROUND  1. Technical Field
 The present application generally relates to nanotube switching circuits and in particular to nanotube switching circuits used in receiver circuits.
 2. Discussion of Related Art
 Digital logic circuits are used in personal computers, portable electronic devices such as personal organizers and calculators, electronic entertainment devices, and in control circuits for appliances, telephone switching systems, automobiles, aircraft and other items of manufacture. Early digital logic was constructed out of discrete switching elements composed of individual bipolar transistors. With the invention of the bipolar integrated circuit, large numbers of individual switching elements could be combined on a single silicon substrate to create complete digital logic circuits such as inverters, NAND gates, NOR gates, flipflops, adders, etc. However, the density of bipolar digital integrated circuits is limited by their high power consumption and the ability of packaging technology to dissipate the heat produced while the circuits are operating. The availability of metal oxide semiconductor ("MOS") integrated circuits using field effect transistor ("FET") switching elements significantly reduces the power consumption of digital logic and enables the construction of the high density, complex digital circuits used in current technology. The density and operating speed of MOS digital circuits are still limited by the need to dissipate the heat produced when the device is operating.
 Digital logic integrated circuits constructed from bipolar or MOS devices do not function correctly under conditions of high heat or heavy radiation. Current digital integrated circuits are normally designed to operate at temperatures less than 100 degrees centigrade and few operate at temperatures over 200 degrees centigrade. In conventional integrated circuits, the leakage current of the individual switching elements in the "off' state increases rapidly with temperature. As leakage current increases, the operating temperature of the device rises, the power consumed by the circuit increases, and the difficulty of discriminating the off state from the on state reduces circuit reliability. Conventional digital logic circuits also short internally when subjected to heavy radiation because the radiation generates electrical currents inside the semiconductor material. It is possible to manufacture integrated circuits with special devices and isolation techniques so that they remain operational when exposed to heavy radiation, but the high cost of these devices limits their availability and practicality. In addition, radiation hardened digital circuits exhibit timing differences from their normal counterparts, requiring additional design verification to add radiation protection to an existing design.
 Integrated circuits constructed from either bipolar or FET switching elements are volatile. They only maintain their internal logical state while power is applied to the device. When power is removed, the internal state is lost unless some type of non-volatile memory circuit, such as EEPROM (electrically erasable programmable read-only memory), is added internal or external to the device to maintain the logical state. Even if non-volatile memory is utilized to maintain the logical state, additional circuitry is
necessary to transfer the digital logic state to the memory before power is lost, and to restore the state of the individual logic circuits when power is restored to the device. Alternative solutions to avoid losing information in volatile digital circuits, such as battery backup, also add cost and complexity to digital designs.
 Important characteristics for logic circuits in an electronic device are low cost, high density, low power, and high speed. Resistance to radiation and the ability to function correctly at elevated temperatures also expand the applicability of digital logic. Conventional logic solutions are limited to silicon substrates, but logic circuits built on other substrates would allow logic devices to be integrated directly into many manufactured products in a single step, further reducing cost.
 Devices have been proposed which use nanoscopic wires, such as single-walled carbon nanotubes, to form crossbar junctions to serve as memory cells. (See WO 01/03208, Nanoscopic Wire-Based Devices, Arrays, and Methods of Their Manufacture; and Thomas Rueckes et al., "Carbon Nanotube-Based Nonvolatile Random Access Memory for Molecular Computing," Science, vol. 289, pp. 94-97, 7 July, 2000.) Hereinafter these devices are called nanotube wire crossbar memories (NTWCMs). Under these proposals, individual single-walled nanotube wires suspended over other wires define memory cells. Electrical signals are written to one or both wires to cause them to physically attract or repel relative to one another. Each physical state (i.e., attracted or repelled wires) corresponds to an electrical state. Repelled wires are an open circuit junction. Attracted wires are a closed state forming a rectified junction. When electrical power is removed from the junction, the wires retain their physical (and thus electrical) state thereby forming a non-volatile memory cell.
 U.S. patent Publication No. 2003-0021966 discloses, among other things, electromechanical circuits, such as memory cells, in which circuits include a structure having electrically conductive traces and supports extending from a surface of a substrate. Nanotube ribbons that can electromechanically deform, or switch are suspended by the supports that cross the electrically conductive traces. Each ribbon comprises one or more nanotubes. The ribbons are typically formed from selectively removing material from a layer or matted fabric of nanotubes.
 For example, as disclosed in U.S. patent Publication No. 2003-0021966, a nanofabric may be patterned into ribbons, and the ribbons can be used as a component to create non-volatile electromechanical memory cells. The ribbon is electromechanically-deflectable in response to electrical stimulus of control traces and/or the ribbon. The deflected, physical state of the ribbon may be made to represent a corresponding information state. The deflected, physical state has non-volatile properties, meaning the ribbon retains its physical (and therefore informational) state even if power to the memory cell is removed. As explained in U.S. patent Publication No. 2003-0124325, three-trace architectures may be used for electromechanical memory cells, in which the two of the traces are electrodes to control the deflection of the ribbon.
 The use of an electromechanical bi-stable device for digital information storage has also been suggested (c.f. U.S. Pat. No. 4,979,149: Non-volatile memory device including a micro-mechanical storage element).
 The creation and operation of bi-stable, nanoelectro-mechanical switches based on carbon nanotubes (including mono-layers constructed thereof) and metal electrodes has been detailed in a previous patent application of Nantero, Inc. (U.S. Pat. Nos. 6,574,130, 6,643,165, 6,706, 402; U.S. patent application Ser. Nos. 09/915093, 10/033323, 10/033032, 10/128117, 10/341005, 10/341055, 10/341054, 10/341130, 10/776059, and 10/776572, the contents of which are hereby incorporated by reference in their entireties).
 The invention provides receiver circuits using nanotube based switches and logic.
 Under one aspect of the invention, a receiver circuit includes a differential input having a first and second input link, and a differential output having a first and second output link. First, second, third and fourth switching elements each have an input node, an output node, a nanotube channel element, and a control structure disposed in relation to the nanotube channel element to controllably form and unform an electrically conductive channel between said input node and said output node. The control structure of the first switching element is in electrical communication with the first input link, and the input node is in electrical communication with a low reference voltage. The output node is in electrical communication with the first output link. The control structure of the second switching element in electrical communication with the second input link, and the input node is in electrical communication with a low reference voltage, and the output node is in electrical communication with the second output link. The output node of the third switching element is in electrical communication with the first output link, and the control structure is in electrical communication with the second output link and the input node is in electrical communication a high reference voltage. The output node of the fourth switching element is in electrical communication with the second output link, and the control structure is in electrical communication with the first output link and the input node is in electrical communication a high reference voltage.
 Under another aspect of the invention, the control structure of the first and second switching elements includes a control (set) electrode and a release electrode, and the first input link is coupled to the control (set) electrode of the first switching element and the release electrode of the second switching element. The second input link is coupled to the control (set) electrode of the second switching element and the release electrode of the first switching element.
 Under another aspect of the invention, the control structure of the third and fourth switching elements includes a control (set) electrode and a release electrode, and the first output link is coupled to the control (set) electrode of the fourth switching element. The second output link is coupled to the control (set) electrode of the third switching element, and the release electrodes of the third and fourth switching elements are coupled to the high reference voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 depicts a receiver circuit according to certain embodiments of the invention;